Chemotaxis of RBL-2H3 cells toward antigen or S1P is inhibited by expression of SphK1. (A) IgE-sensitized vector-expressing (□) or SphK1-expressing (▪) RBL-2H3 cells cultured in the presence of serum were allowed to migrate toward the indicated concentrations of DNP-HSA or fibronectin (FN; 20 μg/mL) for 3 hours. (B-C) RBL-2H3 cells stably expressing vector (□) or SphK1 (▪) cultured in the presence of serum were allowed to migrate toward the indicated concentrations of S1P (B), dihydro-S1P (C), or fibronectin (20 μg/mL) for 2 hours. Data are the means ± SD of triplicate determinations. Similar results were obtained in 3 additional experiments. (D-E) Effect of SphK1 expression on chemotaxis of serum-starved RBL-2H3 cells. RBL-2H3 cells stably expressing vector (□) or SphK1 (▪) were serum-starved overnight and allowed to migrate toward the indicated concentrations of S1P (D), dihydro-S1P (DH-S1P) (E), or fibronectin (20 μg/mL) for 2 hours. Duplicate cultures were also sensitized with IgE and then allowed to migrate toward DNP-HSA (1 ng/mL) for 3 hours (E). Data are the means ± SD of triplicate determinations and are expressed as fold increases compared with vehicle-treated cells. Similar results were obtained in 2 additional experiments.